The present invention relates to a device for measuring light incident on an image forming optical system making use of a plural number of diffraction elements.
A patent application for a light measuring method by means of diffraction elements has been applied to patent by the present inventors in the U.S.A. on Dec. 6, 1973 under Application Ser. No. 422,337 and in West-Germany on Dec. 11, 1973 under Application No.P 2361626.4.
The device in accordance with the present invention is an improvement of the above mentioned applications, being improved so that a certain determined area of the light beam can be measured with weight accorded that area. The present improvement is made when the device in accordance with the above mentioned application is applied to a single reflex camera as a device to carry out a light measurement, putting weight on the light measurement in the central part. The light measurement with weight in the central part means a light measuring method by means of which the weight is put on the light measurement more in the central part of the picture field than in the circumferential part. This light measurement with weight in the central part is carried out normally in such a manner that the output of the light detecting means sensing only the light beam coming from the central part of the picture field is added to the output of the light detecting means sensing the light beam coming from the whole picture field.